Parser: Implement extension GL_AMD_gpu_shader_half_float.

- Add built-in types: float16_t, f16vec, f16mat.
- Add support of half float constant: hf, HF.
- Extend built-in floating-point operators: +, -, *, /, ++, --, +=, -=,
  *=, /=, ==, !=, >=, <=, >, <.
- Add support of type conversions: float16_t -> XXX, XXX -> float16_t.
- Add new built-in functions.

gtests/CMakeLists.txt

@@ -14,6 +14,7 @@ if (TARGET gmock)
     ${CMAKE_CURRENT_SOURCE_DIR}/AST.FromFile.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/BuiltInResource.FromFile.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/Config.FromFile.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/HexFloat.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/Hlsl.FromFile.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/Link.FromFile.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/Pp.FromFile.cpp